Very spotty render. Fireflies?
The best way to trouble shoot a noisy image, is to render all the main colour render passes (Dif, Gloss, Trans, Sub, Emission and AO) out, and inspect each one. You'll see one or two that are really noisy, and then you should be able to adjust your samples to clear them up. 



I'm a big fan of Branch Path Tracing mode, because it lets you reduce samples in passes that don't need it and increase samples in those that do. I'm fairly certain you should be able to get something looking decent for 500 samples, but you may have to redistribute them differently.